SPC AC 221959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Sun Jul 22 2018

   Valid 222000Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   THE GULF COAST STATES AS WELL AS THE NORTHERN AND CENTRAL PLAINS...

   ...SUMMARY...
   Severe storms, primarily capable of damaging winds and large hail,
   will be possible across parts of the Southeast and northern/central
   Plains this afternoon and evening. A few marginally severe storms
   are also possible over a portion of the Middle Atlantic region.

   ...20Z Update...

   ...Central Gulf Coast into FL...
   Very moist and unstable airmass over the region will continue to
   support a severe thunderstorm threat. Recent radar imagery shows the
   outflow surging southward along the east-central FL coast while
   warm-air advection and resultant backbuilding persists farther
   northwest towards the FL Big Bend. Outflow-dominant character to the
   southeastern portion of the this convective complex suggests a
   somewhat diminished severe threat, although isolated damaging wind
   gusts remain possible. Relatively higher threat exists across the
   backbuilding portion of the cluster as storm interactions and new
   updraft development increase the chances for water loading. Moist
   inflow and somewhat stronger southeasterly winds will also support a
   low tornado threat in this region.

   Severe threat also continues across southern AL, southwest GA, and
   adjacent portions of the FL Panhandle. In this area, a more discrete
   storm mode and stronger shear has lead to the development of several
   supercells with the moist and unstable airmass supporting both left
   and right splits. Discrete storm mode and more updraft organization
   has led to a greater threat for hail here than over areas farther
   southeast. Upscale growth into a more coherent convective line which
   then tracks across the central FL Peninsula is possible. Subsidence
   behind the ongoing storms as well as beneath the right exit region
   of the upper jet will likely temper any additional development
   across southern AL. Additional short-term details about this area
   are available in MCD 1136.

   ...Northern/Central Plains...
   Overall scenario outlined in the previous discussion (appended
   below) remains valid with no change needed to the outlook.
   Additional short-term information is available in MCD 1135.

   ...Mid-Atlantic States...
   Observational trends and recent guidance suggest the severe threat
   across SC has dropped below 5% and the outlook was updated
   accordingly. Elsewhere across the region, enhanced mid-level flow
   supports occasional bowing line segments and the potential for
   damaging wind gusts. Additionally, southeasterly surface winds
   across eastern VA result in slightly stronger low-level shear
   (sampled well by recent LWX and AKQ VAD wind profiles) and a low
   tornado risk.

   ..Mosier.. 07/22/2018

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Jul 22 2018/

   ...Gulf Coastal area including Florida...

   Numerous storms are in the process of developing within the weakly
   capped, but moderately unstable environment across northern FL.
   These storms will be capable of producing mainly isolated damaging
   wind. Additional storms are expected to develop/intensify farther
   west along and south of a cold front across southern AL as well as
   in association with sea breeze boundaries over the FL Panhandle.
   These storms will be embedded within 35-45 kt unidirectional
   effective bulk shear within base of upper low circulation. Damaging
   wind and large hail will be possible with both multicell and
   supercell storm modes.

   ...Northern through central Plains region...

   A shortwave trough will continue east through Saskatchewan and
   Manitoba along the international border and eventually affecting
   extreme northern ND. A cold front will accompany this feature
   through the northern and central Plains today and tonight. A
   corridor of moderate instability is likely in pre-frontal warm
   sector along with sufficient (35-45 kt) deep-layer shear for
   supercells from ND into SD. Storms will likely develop over the
   Dakotas later this afternoon posing a risk for isolated large hail
   and damaging wind gusts. Other storms might develop farther south
   along the front across central NE by early evening where weaker
   shear will promote multicells, but the thermodynamic environment
   will support some threat for a few instances of damaging wind and
   large hail. Other storms will form over the higher terrain of CO and
   WY and spread east into the High Plains this afternoon and evening
   with a modest threat for damaging wind and hail.

   ...Middle Atlantic region...

   Some destabilization is likely in this region today and potential
   will exist for storms to redevelop and interact with a weak warm
   front as they lift north. Low-level hodographs in vicinity of this
   boundary will support a modest risk for a few low-level
   mesoscyclones and a brief tornado or two. Reference SWOMCD 1132 for
   more information.

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